Abstract: A method for increasing impedance range of string-based force feedback device by adjusting the pretighting force dynamically is proposed.The basic structure of string-based force feedback device is presented,and an energy-dissipation-based approach is used to analyze the influence of string tension on the stability of haptic display when rendering high-stiffness virtual objects.And the relationship between string pretightening force and force interaction transparency is analyzed.In order to meet the requirements of stability and transparency simultaneously,string pretighting force is adjusted dynamically according to the contact state between the end-effector and virtual objects.Experimental results show that this method can tradeoff stability and transparency,thereby enlarge the achievable impedance range.